Field of the Invention
The present disclosure relates to a light emitting diode chip and a light emitting diode package including the same and, more particularly, to a light emitting diode chip for high voltage operation and a light emitting diode package including the same.
Discussion of the Background
Compound semiconductor light emitting diodes (also referred to as “LEDs”), for example, III-V based LEDs, are widely used for display devices. Particularly, with merits of lower power consumption and longer lifespan than existing electric bulbs or fluorescent lamps, GaN LEDs are applicable not only to backlight sources but also to general lighting by replacing the existing incandescent lamps and fluorescent lamps.
An LED is repeatedly turned on/off depending on the direction of a current by an AC power source. Thus, when the LED is directly connected to the AC power source, there is a problem in that the LED does not continuously emit light and is liable to be damaged by the reverse current. Moreover, the LED has a low driving voltage of 3˜4 V and thus cannot be directly connected to any high voltage power source like general power sources for domestic use, such as 110 V or 220 V.
In order to solve such problems of the LED, an LED that can be used by being directly connected to a high voltage AC power source is disclosed in International Publication No. WO 2004/023568 (A1), entitled “Light-emitting device having light-emitting elements” by Sakai et. al., and various other LEDs for the AC power source have been developed.
According to the PCT International Publication No. WO 2004/023568 (corresponding to U.S. Patent Application Publication No. 2005/0253151), LED elements are two-dimensionally arranged on an insulating substrate, for example, a sapphire substrate, and are connected in series to form an LED array. Two such LED arrays are connected in reverse parallel to each other on the sapphire substrate, thereby providing a single light emitting device that can be operated to continuously emit light using a high voltage AC power supply.
According to the PCT International Publication No. WO 2004/023568, one of the two arrays is operated during a half-period of the AC power source and the other array is operated during the subsequent half-period. In other words, half light emitting cells, that is, half LED elements, in the light emitting diode are operated during phase variation of the AC power source. Thus, utilization efficiency of the light emitting cells does not exceed 50%.
Meanwhile, it is known in the art that a light emitting diode consisting of a single light emitting cell has a longer lifespan than others. However, the LED array is formed by connecting a plurality of light emitting cells in series via wires, so that the lifespan of the light emitting diode depends not only on lifespan of each of the light emitting cells but also on characteristics of the wires and ohmic contacts. In other words, failure of any one of the light emitting cells in the LED array, breakage or short-circuit in any one of the wires, or failure in any one of the ohmic contacts entails failure of the light emitting diode. Moreover, the driving voltage of the LED array is obtained as the sum of a voltage drop in the light emitting cells and a voltage drop caused by resistance of the wires connecting the light emitting cells, ohmic contact resistance, and the like. Accordingly, the driving voltage of the LED array including the light emitting cells exhibits greater deviation than that of the light emitting diode consisting of a single light emitting cell. Such a deviation of the driving voltage can affect reliability, lifespan and the like of the light emitting diode including the LED arrays.
In order to evaluate reliability of an LED, various properties of the LED, such as optical and electric properties, are measured. Particularly, leakage current caused by application of a reverse voltage to the LED is a major item for reliability evaluation of the LED. For an LED including LED arrays connected in reverse parallel to each other, however, there is a problem that the leakage current is not measured upon application of the reverse voltage to one LED array. Therefore, there is a need for a new method for selective separation of reliable LEDs.